g-mail smtp is returning this error: "Verify that you have addressed this message correctly. Check your SMTP server settings in Mail preferences and verify any

g-mail smtp is returning this error: "Verify that you have addressed this message correctly. Check your SMTP server settings in Mail preferences and verify any advanced settings with your system administrator. The server response was: The recipient address <'*+-/=?^_`{|}~#$@[ipv6:2001:470:30:84:e276:63ff:fe72:3900]> is not a valid RFC-5321 address. <...> - gsmtp" Not even Google engineers can get it right. We are doomed.